The present invention relates to a multilayer wiring board and, more particularly, to a multilayer wiring board in which a through hole passes through a ground layer or a power source layer.
A conventional multilayer wiring board of this type includes a signal wiring layer, a ground layer, and a power source layer. The ground layer and the power source layer supply a predetermined potential to an electronic part mounted on a multilayer wiring board and also set the characteristic impedance of a wiring pattern in the signal wiring layer to a predetermined value. In the portion of the multilayer wiring poard where a through hole passes through without being connected to the ground layer or the power source layer, a capacitive component is generated between the ground layer or the power source layer and the through hole. Reflection noise occurs due to the capacitive component and, as a result, the waveform of a signal transmitted through the through hole is distorted. Consequently, signals having frequencies of 100 mega-hertz (MHz) or higher cannot be transferred.
Also, in order to increase the number of signal wiring patterns in the multilayer wiring board, the number of signal wiring layers is increased. As the number of signal wiring layers increases, the number of the ground layers and the number of power source layers inevitably increase. Consequently, the total capacitance of the capacitive components existing on the signal transmission path and generated between the ground layers or the power source layers and the through hole also increases.
Japanese Patent Application Laid-Open Hei No. 5-102667 discloses a multilayer wiring board which addresses the problem described above. A wiring pattern printed in a signal wiring layer and a through hole are connected via a connecting member having a large inductive component. The connecting member is formed so that it is narrower toward the through hole to increase the inductive component. According to the multilayer wiring board disclosed in the publication, the capacitive reflection noise is cancelled out by inductive reflection noise caused by the connecting member.
However, the multilayer wiring board has reliability problems and is expensive to manufacture. The connecting part where the signal wiring pattern is connected to the through hole breaks easily, thereby decreasing manufacturing yields. This occurs because the signal wiring pattern is narrower toward the through hole to increase the inductive components in the part.